The kraft pulping of lignocellulosic material in the form of wood chips usually entails the reaction and dissolution by an alkaline liquor (white liquor) of lignin which serves as a binder for the cellulosic material. The dissolution of this binder serves to liberate the fibres, which are separated from the residual cooking liquor, which is known in the art as black liquor. The black liquor, which contains inorganic compounds resulting from the cooking chemical along with the dissolved wood components is first concentrated by evaporation and is then fed to a recovery furnace where organic wood components are burnt with the evolution of heat, while the inorganic components are subjected to a reduction stage in the furnace. The inorganic residue from the furnace is called smelt. The smelt derived from a kraft pulping process contains soda ash (sodium carbonate) and sodium sulfide.
Kraft recovery furnaces usually represent a substantial capital investment with fixed capacity. Accordingly, few viable options exist for pulping chemicals recovery for a kraft mill wishing to increase its volume of production where the recovery furnace is running at capacity.
It is therefore an object of the present invention to provide a process which permits an increase in the capacity for inorganics recovery for kraft furnaces which are already running at capacity.